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When converting phi nodes into select instructions, we shouldn't promote PHI

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nodes unless we KNOW that we are able to promote all of them.  In this case
promoting the phi to a select is silly because we will always have to do the
call conditionally.  As such, select promotion is actually a pessimization.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16972 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-10-14 05:12:50 +00:00
parent 83d3aad50e
commit 1c7efba2bd
1 changed files with 29 additions and 0 deletions
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29
test/Transforms/SimplifyCFG/PhiNoEliminate.ll Normal file
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; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | not grep select
;; The PHI node in this example should not be turned into a select, as we are
;; not able to ifcvt the entire block. As such, converting to a select just
;; introduces inefficiency without saving copies.
int %bar(bool %C) {
entry:
br bool %C, label %then, label %endif
then:
%tmp.3 = call int %qux()
br label %endif
endif:
%R = phi int [123, %entry], [12312, %then]
;; stuff to disable tail duplication
call int %qux()
call int %qux()
call int %qux()
call int %qux()
call int %qux()
call int %qux()
call int %qux()
ret int %R
}
declare int %qux()